Information is sent via a communication channel. A transmitter may communicate the information by modulating a carrier signal (e.g., a wireless carrier). A receiver may demodulate the carrier signal to recover the information. The carrier signal must have sufficient power to ensure that the receiver can demodulate the carrier signal. An example of a carrier signal is an uplink communications carrier signal which may be sent from a transmit terminal at an uplink station to a space based satellite which may then retransmit the signal via downlink communication carrier signal to a receive terminal at a receive station.
Wireless carriers are subject to fluctuating received power levels due to changes in atmospheric conditions. For example, in satellite communications, transmitted carriers can be affected by changes in the atmospheric conditions on both sides of the communication link (earth to satellite and satellite to earth). This is shown in FIG. 1, which shows the variation in attenuation that a 27 GHz and a 20 GHz carrier signal may experience over time. Atmospheric changes maybe caused by rain, snow, hail, ice, clouds and moisture. In many instances, these changes can cause significant degradation to the received power level of the carrier signals (such as the uplink signal) and result in poor quality of reception.
The most common approach to correct for the received power level problem is to monitor a non-communications signal and then adjust the transmit carrier power based on the measured degradation in such a non-communications signal. As in the example above the space based satellite may send the non-communication signal (such as a beacon signal, or a pilot tone) to a receive terminal at the uplink station. Although this method can sometimes be effective, degradation that is experienced by the non-communication signal does not always correlate well with degradation experienced by the uplink carrier signals. In addition, fluctuations experienced by carriers in a wireless channel can be highly unpredictable and rapid, causing the power control scheme to lag significantly behind the signal degradation, thus rendering power corrective actions ineffective.